Cluster bombs: metabolic syndrome tied to heart disease deaths.

Men with a certain cluster of metabolic characteristics are about three times as likely to die of heart disease as men without the traits are, according to a new study.

The cluster, called the metabolic syndrome or syndrome X, is made up of generally mild risk factors that often occur together, says Hanna-Maaria Lakka, who is currently at Pennington Biomedical Research Center in Baton Rouge, La. These features include high blood pressure, high triglyceride concentrations in the blood, abnormal metabolism of blood sugar, and excess weight, especially around the waist (SN: 4/8/00, p. 236).

"By themselves, these risk factors may seem unimportant and are often overlooked," says Lakka. "But together, they pose a serious risk."

Past studies have linked elevated risks of heart disease, stroke, and diabetes to the metabolic syndrome, which shows up in about one in three middle-age people in the United States. In the new study, Lakka and her colleagues at the University of Kuopio in Finland looked for a connection between the syndrome and death from heart attacks.

Between 1984 and 1998, the researchers followed each of 1,209 Finnish men for an average of more than 11 years. All volunteers were initially between 42 and 60 years old and free of heart disease, diabetes, and cancer.

From tests at the beginning of the study, the researchers identified which men met criteria of the metabolic syndrome. Between 8.8 and 14.3 percent of the volunteers had the syndrome, depending on which of four slightly different definitions the scientists used.

During the study, heart disease caused 27 deaths among the volunteers. Participants who began the study with the metabolic syndrome were between 2.9 and 4.2 times as likely to die of heart disease as were those without it. The range represents different definitions of the syndrome. Lakka and her colleagues report their findings in the Dec. 4 Journal of the American Medical Association.

The researchers also conducted an analysis that excluded volunteers whose control of blood sugar concentration was impaired, a condition that often leads to diabetes. A strong association between the metabolic syndrome and death from heart disease persisted, suggesting that the link doesn't depend on the syndrome's role in diabetes, the researchers assert.

"Across the different definitions [of the syndrome], their results are incredibly consistent," says Angela D. Liese, a nutritional epidemiologist at the University of South Carolina in Columbia. While past research strongly suggested that having the metabolic syndrome would be a risk factor for death from heart disease, "it's one thing to expect [a negative health] outcome and another to see it, she says.

However, Gerald Reaven of Stanford University School of Medicine considers the new study "much ado about nothing? Reaven, a pioneer in describing the metabolic syndrome, suggests that the diagnosis may have outlived its usefulness, since studies have found that many of the factors included in the metabolic syndrome independently predict heart disease.

In a related paper in the December American Journal of Epidemiology, Lakka and her collaborators compare the diabetes-predicting power of various definitions of the metabolic syndrome. A definition that factors in waist-to-hip ratio and body-mass index was most likely to identify people who would later develop diabetes.

However, because health risks from metabolic disorders vary along a continuum, a simple yes-or-no diagnosis of the metabolic syndrome is of limited use to physicians, Reaven says.

Liese still sees value in recognizing the metabolic syndrome. "Typically, people have more than one of these risk factors" if they have any at all, she says. These disorders should be monitored and treated together, she argues.